Printed circuit board providing heat dissipation

ABSTRACT

A printed circuit board includes an insulated base sheet, a heat-conducting layer, and a plurality of heat-conducting blocks. The heat-conducting layer is disposed on the insulated base sheet. The heat-conducting blocks are formed on the heat-conducting layer. Each of the heat-conducting blocks is separated from each other.

BACKGROUND

1. Field of the Invention

The present invention generally relates to printed circuit boards, andparticularly, to a printed circuit board providing heat dissipation.

2. Discussion of the Related Art

Printed circuit boards (PCB) are commonly employed as a base or carrierfor circuit elements such as microprocessor chips, power dietransistors, semiconductors and other circuit components. Presently,many electronic assemblies require small volume, with the PCB requiringthe same, such that circuit elements must be densely assembled thereon.As a result, heat produced by the circuit elements is accumulated on thePCB, presenting difficulty in the dissipation thereof. Thus, the circuitelements have an unduly short functional lifespan. Such PCBs generallyincorporate a system for heat dissipation, such as a heat dissipationhole defined in the PCB, a metallic layer formed on the PCB, a metallicsheet attached to a rear portion of the PCB, or a layer of thermalgrease.

A typical PCB includes an insulated sheet, copper foil formed on thesheet, and a solder mask partially coating the copper foil. Areas of thecopper foil not coated with solder mask form a plurality of cross-shapedcopper zones. When the PCB is placed into a tin stove, tin alloy isformed on the copper zones in corresponding cross-shaped tin strips,providing heat dissipation. However, the tin strips occupy a relativelylarge area, occupying valuable footprint space, and, in fact, if circuitelements need to be densely mounted on the PCB, there will be not enoughroom for formation of the tin strips. Accordingly, the tin strips offeronly limited efficacious benefit.

Therefore, a printed circuit board providing heat dissipation is desiredto overcome the described limitations.

SUMMARY

A printed circuit board includes an insulated base sheet, aheat-conducting layer, and a plurality of heat-conducting blocks. Theheat-conducting layer is disposed on the insulated base sheet. Theheat-conducting blocks are mounted on the heat-conducting layer. Theheat-conducting blocks are separated from each other.

Other advantages and novel features will become more apparent from thefollowing detailed description when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The components in the drawings are not necessarily drawn to scale, theemphasis instead being placed upon clearly illustrating the principlesof a printed circuit board providing heat dissipation. Moreover, in thedrawings, like reference numerals designate corresponding partsthroughout the several views.

FIG. 1 is a top plan view of one side of a first exemplary embodiment ofa printed circuit board providing heat dissipation.

FIG. 2 is a partial cross-section of the printed circuit board of FIG.1, taken along the line II-II thereof.

FIG. 3 is an enlarged top plan view of one side of a second exemplaryembodiment of a printed circuit board providing heat dissipation.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Reference will now be made to the drawings to describe embodiments ofthe printed circuit board in detail.

Referring to FIGS. 1 and 2, a printed circuit board 10 of a firstembodiment includes an insulated base sheet 11, a heat-conducting layer12, an insulated layer 13, a plurality of separate heat-conductingblocks 14, and a plurality of bonding pads 15. The insulated base sheet11 is glass-filled epoxy, Kevlar, or phenolic resin. The heat-conductinglayer 12 is preferably a copper foil formed on the insulated base sheet11. It is to be noted that the heat-conducting layer 12 can also bealuminum foil or other heat-conducting metallic material. The insulatedlayer 13 is a solder mask partially coated on the heat-conducting layer12. The heat-conducting blocks 14 on the heat-conducting layer andpreferably tin alloy. The bonding pads 15 are disposed on theheat-conducting layer 12 for soldering circuit elements.

In a method for fabricating the heat-conducting blocks 14, insulatedlayer 13 is coated on a surface of heat-conducting layer 12, covering itcompletely. A portion of the insulated layer 13 is removed from theheat-conducting layer 12, creating a plurality of exposed zones 121thereon. The exposed zones 121 are metallic surfaces. In a tin stove,tin alloy is coated on the exposed zones 121 to form a plurality ofsolid heat-conducting blocks 14 for heat dissipation. The exposed zones121 are separated and can be circular, elliptical, or polygonal,preferably circular and of uniform radius. Each of the heat-conductingblocks 14 preferably extends out of the insulated layer 13 and includesa spherical top portion 141.

Separation of the bonding pads 15 by relatively large spaces results ina correspondingly large empty surface on the insulated layer 13. Theheat-conducting blocks 14 are arrayed regularly on the empty surface.The size of each exposed zone 121 affects the rate of heat dissipation.If each exposed zone 121 is too small, heat-conducting blocks 14 formedthereon will be too small to optimize the effect of heat dissipation. Ifthe exposed zone 121 is too large, the number of heat-conducting blocks14 formed on the printed circuit board 10 will be decreased, therebyweakening the effect of heat dissipation. When exposed zones 121 arecircular, the radius D of each exposed zone 121 should preferably befrom about 1.2 to 2.0 millimeters (mm). In the first embodiment, theradius D of each exposed zone 121 is 1.6 mm. Each of the heat-conductingblocks 14 is separated from its adjacent heat-conducting block 14 at aninterval L1 exceeding about 0.5 mm.

Referring to FIG. 3, in a second embodiment, the bonding pads 15 aredensely positioned on the insulated layer 13, making it difficult tofind a relatively large empty surface. The heat-conducting blocks 14 arepositioned in empty areas of the insulated layer 13 adjacent to thebonding pads 15. To prevent solder such as tin alloy from inadvertentlycontacting the bonding pads 15, a minimum distance L2 between an edge ofeach exposed zone 121 and an edge of its adjacent bonding pad 15 ispreferably equal to or exceeding about 0.3 mm.

In use, heat produced by circuit elements is quickly transmitted by theheat-conducting layer 12 to the heat-conducting blocks 14 and theheat-conducting blocks 14 dissipate the heat, thus the printed circuitboard 10 exhibits good heat dissipation. The heat-conducting blocks 14can be positioned in empty areas of the insulated layer 13 adjacent tothe bonding pads 15 and do not interfere with the layout of the printedcircuit board 10, suiting them well for deployment on high densityintegrated PCBs.

It is believed that the present embodiments and their advantages will beunderstood from the foregoing description, and it will be apparent thatvarious changes may be made thereto without departing from the spiritand scope of the invention or sacrificing all of its materialadvantages, the examples hereinbefore described merely being preferredor exemplary embodiments of the invention.

1. A printed circuit board, comprising: an insulated base sheet; aheat-conducting layer disposed on the insulated base sheet; an insulatedlayer partially coated on the heat-conducting layer, leaving a pluralityof exposed zones remaining thereon; and a plurality of circularheat-conducting blocks formed on the heat-conducting layer, each of theheat-conducting blocks being separated from each other, and theheat-conducting blocks being correspondingly arrayed on the exposedzones of the insulated layer.
 2. The printed circuit board of claim 1,wherein all of the exposed zones have a same radius.
 3. The printedcircuit board of claim 2, wherein a radius of each exposed zone is fromabout 1.2 mm to about 2.0 mm.
 4. The printed circuit board of claim 3,further comprising a plurality of bonding pads positioned on theheat-conducting layer for soldering circuit elements, wherein a minimumdistance between an edge of each exposed zone and an edge of itsadjacent bonding pad is equal to or exceeding about 0.3 mm.
 5. Theprinted circuit board of claim 1, wherein each of the heat-conductingblocks extends out of the insulated layer and includes a spherical topportion.
 6. The printed circuit board of claim 1, wherein each of theheat-conducting blocks is separated from its adjacent heat-conductingblock by an interval exceeding 0.5 mm.
 7. The printed circuit board ofclaim 1, wherein the insulated base sheet is glass-filled epoxy, Kevlar,or phenolic resin.
 8. The printed circuit board of claim 1, wherein theheat-conducting layer is copper foil formed on the insulated base sheet.9. The printed circuit board of claim 1, wherein the heat-conductinglayer is aluminum foil formed on the insulated base sheet.
 10. Theprinted circuit board of claim 1, wherein the heat-conducting blocks aretin alloy.
 11. The printed circuit board of claim 1, wherein theinsulated layer is solder mask.